Malaria caused by Plasmodium spp parasites is a leading infectious disease killer in the developing world. In the face of developing resistance against the current last-line therapy, new antimalarials are desperately needed and a greater understanding of Plasmodium biology will be required to identify viable therapeutic targets. The apicoplast, a unique prokaryotically-derived plastid organelle found in Plasmodium, holds promise for both drug and vaccine development as it is essential for every stage in the parasite's complex life cycle. Yet despite its importance to parasite survival and the identification of several biosynthetic pathways in the organelle, the function of the apicoplast during infection remains unclear. Our long-term objective is to identify the specific proteins and pathways involved in apicoplast function for therapeutic and vaccine development. The goal of this proposal is to decipher the role of the apicoplast-located isoprenoid precursor biosynthetic pathway in blood-stage P. falciparum infection. This pathway is of particular interest because it 1) is prokaryotic and therefore not found in the human host, 2) may be essential for blood-stage growth, 3) may be the only cytoplasmic metabolite derived from the apicoplast during blood stage growth, and 4) is required for the biosynthesis of cellular isoprenoids with a host of potential downstream functions that could be unique to the parasite. The specific aims are: 1) to determine the essentiality and sufficiency of isoprenoid precursor biosynthesis for fulfilling apicoplast function during blood-stage infection and 2) to identify the cellular isoprenoids derived from isoprenoid precursors during blood stage infection. We propose innovative chemical biology approaches to probe the function of this pathway. The outcome of these aims will represent a significant advance in our understanding of isoprenoid precursor biosynthesis in apicoplast function and blood-stage P. falciparum infection. This knowledge has the potential to reveal novel aspects of Plasmodium pathogenesis and facilitate identification of specific candidates for antimalarial drug development. The proposed research is part of a mentored career development plan for an academic career in microbial pathogenesis and parasitology. The principal investigator is a PhD-trained biochemist/chemical biologist and infectious disease pathologist completing Clinical Pathology residency training. My goal as an independent researcher is to apply chemical biology approaches to the study of malaria pathogenesis. Dr. Joe DeRisi, who has been at the forefront of the application of genomic technology to the study of Plasmodium biology, will serve as a mentor for this project. The career development plan also includes the appointment of an advisory committee, classes and seminars in microbial pathogenesis, and presentation at international malaria conferences. The proposed research and career development activities will be critical in the preparation for an academic career and provide ample opportunities for a future in independent research. Project Narrative Malaria is a leading global infectious disease killer, and new drug therapies are desperately needed in the face of developing resistance against the current last-line therapy. An unusual prokaryotically-derived organelle called the apicoplast has promise for both drug and vaccine development against malaria, but little is known regarding its function(s) during infection. This proposal elucidates the role of a key pathway in the apicoplast during blood-stage infection to begin to define organelle function and realize its potential as a therapeutic target.